1. Field of the Invention
The present invention relates to bituminous roofing products such as asphalt-based roofing membranes and processes for making such roofing products.
2. Brief Description of the Prior Art
Asphalt-based roofing membranes are excellent waterproofing materials that have been extensively used in low-slope roofing systems to provide long-lasting and satisfactory roof coverings. Low-slope roofing systems are extensively used for commercial and industrial buildings. Examples of low-slope roofing systems are built-up roofs (BUR), modified bitumen roofs, and single-ply or membrane roofing systems. Asphalt-based roofing membranes are frequently used as waterproofing underlayment in low-rise roofing systems, as well as the uppermost or finish layer in built-up-roofs. Built-up roofs are sometimes covered with a layer of gravel or granular mineral material to protect the roofing membrane against mechanical damage.
Typically, bituminous roofing products are sheet goods that include a non-woven base or scrim formed of a fibrous material, such as a glass fiber mat. The base is coated with one or more layers of a bituminous material such as asphalt to provide water and weather resistance to the roofing product. Depending on the application, one side of the roofing product may be coated with mineral granules to provide durability, reflect heat and solar radiation, and to protect the bituminous binder from environmental degradation. Roofing granules can be embedded in the surface of such bituminous roofing products using conventional methods.
Mineral-surfaced asphalt shingles, such as those described in ASTM D225 or D3462, are generally used for steep-sloped roofs to provide water-shedding function while adding aesthetically pleasing appearance to the roofs. Conversely, roll goods such as asphalt-based roofing membranes are generally used for low-slope roofs. Pigment-coated mineral particles are commonly used as color granules in roofing applications to provide aesthetic as well as protective functions. Roofing granules are generally used in asphalt shingles or in roofing membranes to protect asphalt from harmful ultraviolet radiation.
Roofing products such as asphalt shingles and roll stock are typically composite articles including a non-woven glass fiber or felt web covered with a coating of water repellent bituminous material, and optionally surfaced with protective mineral-based roofing granules.
Asphalt based roofing products have the challenge of meeting demanding fire resistance requirements set forth by national and international codes. One way in which fire resistance is improved is by adding fire retardant chemicals to the asphaltic materials. Another way in which fire resistance can be improved is by coating roofing products with coatings compositions including fire retardant chemicals.
For example, a self-adhesive roofing membrane can consist of a polyester mat that has been coated on its upper side with polymer-modified asphalt. The fire resistance of the polymer-modified asphalt coating can be increased by including limestone fillers, or fire retardant chemicals, depending on the fire resistance requirement. The under side of the polyester mat can include a polymer-modified asphalt coating that has been further modified with various tackifying resins and plasticizing oils to become self-adhesive. In addition, the lower layer may contain limestone filler, or fire resistance chemicals. However, such materials are usually used sparingly because they tend to reduce the adhesive properties of the bottom layer. Self-adhesive roofing membranes are usually applied over other layers of roofing membrane to provide roofs with long lasting protection against water leakage.
The fire resistance properties of roofing systems are typically measured using Underwriters' Laboratories 790 test method, Tests for Fire Resistance of Roof Covering Materials, which includes three test procedures, spread of flame, intermittent flame, and burning brand tests. This test employs a roof deck that slopes upward from the source of flame. When exposed to vigorous flames and high temperatures, the asphalt coating and the polyester mat of a typical self adhesive roofing membrane start burning and melting. In addition, the bottom coating of the product in the example melts particularly quickly reflecting the presence of various tackifying resins and plasticizing oils which render the layer self-adhesive. Even when this layer contains fire resistance chemicals melting of asphalt does occur. When this happens, molten asphalt starts running downward towards the flame and catches on fire dribbling from the edges while burning. This behavior constitutes a failure as far as UL790 is concerned. It would be advantageous if the bottom layer could be divorced from the flames, and kept isolated.
Laminated single-ply roofing membranes are known, such as those disclosed in U.S. Pat. Nos. 6,502,360; 5,456,785; 5,620,554; and 5,643,399. U.S. Pat. No. 6,296,912 discloses a roofing membrane having a fibrous layer on top for providing a secure surface for roof installation personnel.
Multilayer roofing membranes reinforced with polymeric materials are known. Such membranes are available, for example, faced with polyethylene film, or with mineral particles bonded to an underlying polyethylene film.
U.S. Pat. No. 4,287,248 discloses a bituminized roofing sheet with improved flame resistance. The roofing sheet consists of a reinforced fleece, bitumen, and a metal foil placed on one face of the sheet. U.S. Pat. No. 5,000,999 discloses a bituminized roofing sheet having a metal foil applied to the bottom of the lower layer and optionally to the upper surface of the roofing sheet.
There is a continuing need for roofing materials that have improved resistance to fire while providing good weatherproofing characteristics. In addition, there is a continuing need to provide improved resistance to fire while reducing the addition of expensive fire resistance chemicals.